Opacities in the eye are primarily caused by cataract which is globally the leading cause of blindness, whereas hardening of the lens is primarily related to presbyopia. Presbyopia is defined as a decrease in accommodative amplitude of the eye resulting in an inability to correctly focus light on the retina from objects at variable distance. This is usually noticed by emmetropic subjects (persons who do not need spectacle or contact lens correction for distance vision) between age 40-50 as inability to see close objects clearly.
When an human is born, the lens is transparent even to ultraviolet and the dense protein content of the lens forms a well-organised, elastical and flexibles substance. From the age of 10 years, progressive yellowing begins to change the lens, concurrently or in close relation to the loss of accommodative amplitude. Ultimately, in the 7th or 8th decade of life, a large proportion of subjects will have developed visual impairment secondary to cataract, i.e. opacification of the lens.
On a global level, thousands of people are blinded each year by cataract and at present the only cure is removal of the lens by surgery. For many people surgery is not an option because of lack of access to modern standards of surgical treatment. Even in industrialized countries the burden of treatment creates significant problems for the health care systems. Thus, an instrument for restoration of visual function (accommodative amplitude and clarity) by treatment of the lens, preferably non-invasive, will be of significant value for the prevention and treatment of visual dysfunction.
The yellow coloration of the lens is believed to be caused by the formation of covalent cross-links and aggregation of degraded proteins in the lens. Molecular cross-links and other types of degradation disrupt the optical and mechanical properties of the lens. The fluorescence of cyclic molecular components of the cross-links is early evidence of this process.
The application of laser light for photomanipulation of the eye is well known in the field of opthalmology. In this context laser light is understood as light which is sufficiently monochromatic to allow sufficient focus. One example of the application of laser light is U.S. Pat. No. 6,322,556 where laser light is applied to ablate and thereby remove small portions of the lens with the purpose of correcting vision. A different application is described in U.S. Pat. No. 6,726,679 where laser light is applied to dissolve opacities and/or hardenings of an unopened eye. However this method has several drawbacks. Firstly, with the eye closed it is not possible to determine exactly where in the lens the eye is being treated, which in turn may result in damages as the same position may mistakenly be treated several times. Secondly, the correct dose of laser light applied to a position within the eyes to achieve a significant clinical result is highly individual and may vary with the position in the lens. With set values of the laser this may result in ineffective under-treatment or damaging over-treatment. Damages may occur due to local evaporation of the constituents in the lens resulting in gas blisters (cavitation bubbles). Such blisters are considered unavoidable and in some instances preferable in U.S. Pat. No. 6,726,679, however their appearance and collapse may induce significant mechanical stress on the lens and/or surrounding tissue, so the formation of gas blisters should be avoided, or be avoidable, in a manner that can be controlled by the treating physician or therapist or an automated therapeutic instrument. On the other hand, when using methods such as described in U.S. Pat. No. 6,726,679 it is difficult to adjust the amount of energy, so as to obtain sufficient treatment effect while avoiding or minimizing undesired effects, such as gas blisters or photodamage of the cornea or the living layers of the lens. In spite of these risks, there is no doubt that the non-invasive reduction or removal of opacity and hardenings in the lens is an important clinical goal. It is therefore an object of the present invention to provide a method and apparatus for non-invasive photomanipulation of the lens and/or its constituents, collectively or selectively, while ensuring efficiency and/or ensuring that only the minimally- or non-disruptive amount of photonic energy is transmitted to the eye.